1. Field of Invention
The disclosure herein relates in general to rolling cone earth boring bits, and in particular to improving the performance of a steel tooth bit.
2. Description of Prior Art
Drilling systems having earth boring drill bits are used in the oil and gas industry for creating wells drilled into hydrocarbon bearing substrata. Drilling systems typically comprise a drilling rig (not shown) used in conjunction with a rotating drill string wherein the drill bit is disposed on the terminal end of the drill string and used for boring through the subterranean formation.
Drill bits typically are chosen from one of two types, either drag bits or roller cone bits. Rotating the bit body with the cutting elements on the outer surface of the roller cone body crushes the rock and the cuttings may be washed away with drilling fluid. One example of a roller cone bit 11 is provided in a side partial perspective view in FIG. 1, the bit 11 having a body 13 with a threaded attachment 15 on the bit 11 upper end for connection to a drill string (not shown). The bit 11 further includes legs 18 extending downward from the bit body 13. Each bit leg 18 is shown having a lubricant compensator 17.
The bit body 13 is further illustrating having a nozzle 19 for directing pressurized drilling fluid from within the drill string to cool and lubricate bit 11 during drilling operation. A plurality of cutters 21 are rotatably secured to respective bit legs 18. Typically, each bit 11 has three cutters 21, and one of the three cutters is obscured from view in FIG. 1.
Each cutter 21 has a shell surface including a gauge surface 25 and a heel region indicated generally at 27. Teeth 29 are formed in heel region 27 and form a heel row 28 of teeth. The heel teeth 29 depicted are of generally conventional design, each having leading and trailing flanks 31 which converge to a crest 33. Each tooth 29 has an inner end (not shown) and an outer end 35 that join to crest 33.
Typically steel tooth bits are for penetration into relatively soft geological formations of the earth. The strength and fracture toughness of the steel teeth permits the use of relatively long teeth, which enables the aggressive gouging and scraping actions that are advantageous for rapid penetration of soft formations with low compressive strengths. However, geological formations often comprise streaks of hard, abrasive materials that a steel-tooth bit should penetrate economically without damage to the bit. Although steel teeth possess good strength, abrasion resistance is inadequate to permit continued rapid penetration of hard or abrasive streaks. Consequently, it has been common in the arts since at least the 1930s to provide a layer of wear-resistance metallurgical material called “hardfacing” over those portions of the teeth exposed to the severest wear. The hardfacing typically consists of extremely hard particles, such as sintered, cast, or macrocrystalline tungsten carbide, dispersed in a steel matrix.
Typical hardfacing deposits are welded over a steel tooth that has been machined similar to the desired final shape. Generally, the hardfacing materials do not have a tendency to heat crack during service which helps counteract the occurrence of frictional heat cracks associated with carbide inserts. The hardfacing is much harder than the steel tooth material, therefore the hardfacing on the surface of steel teeth makes the teeth more resistant to wear.
A front view of a cutter 21 is illustrated in FIG. 2. Shown formed on the cutter 21 is an inner row 36 having inner row teeth 37 extending radially inward from the heel 27. The inner row teeth 37 have flanks 31 and crests 33 similar to those of the heel teeth 29. An apex 38 is shown proximate to the cutter 21 center, the apex 38 having grooves 39 radially extending from the apex 38 midpoint to its outer periphery. The cutter 21 further includes scrapers 41 on the heel row 28 between the base of adjacent teeth 29. A layer of hardfacing 35 is shown having been applied to surfaces of the heel teeth 29 and the inner row teeth 37.